This invention relates to an engine starter apparatus and more particularly to an armature coil arrangement of an electric motor for an engine starter apparatus.
Japanese Patent Laid-Open No. 63-181643 discloses one example of a conventional engine starter apparatus for starting an automotive engine in which a hollow armature rotary shaft is provided. In FIG. 1, which illustrates the conventional coaxial starter apparatus disclosed in the above Japanese reference, reference numeral 1 designates an armature of a d.c. electric motor, 2 is an armature core, 3 is an armature rotary shaft which is hollow and having formed therein wedge-shaped cams 3a constituting an over-running clutch function, and the armature core 2 is press-fit over the outer periphery of the rotary shaft 3. 4 is a face-type commutator mounted on the outer circumference of the rear portion of the rotary shaft 3. The commutator surface directly in sliding contact with brushes 5 is formed in a surface perpendicular to the rotary shaft 3. The commutator 4 is connected to an armature coil 6 wound on the core 2. The brushes 5 are forwardly urged by springs 5a behind the brushes 5 and the tips of the brushs 5 are brought into a pressure contact with the sliding contact surface of the commutator 4. A plurality of permanent magnets 7 for generating a magnetic field in the armature 1 are each secured on the inner circumference of the yoke 8 defining a magnetic path. The rear end of the yoke 8 is fitted to the rear bracket 9, and the front end of the yoke 8 is fitted to the front bracket 10. 11 is a bearing mounted to the rear end of the rotary shaft 3 and is supported by the rear bracket 9.
Reference numeral 12 represents rollers placed on the cam 3a formed in the inner surface of the rotary shaft 3 for providing an over-running function together with roller springs. 13 is a clutch inner member of the over-running mechanism which is provided with a bearing 14 at the outer circumference of the intermediate portion for supporting the front end of the rotary shaft 3. 15 is a bearing fitted inside of the front bracket 10 for supporting the front end of the clutch inner member 13. 13a are helical splines formed in the inner surface of the clutch inner member 13, which are in axial sliding engagement with helical splines 16c formed in the outer circumference of the intermediate portion of a pinion shaft 16 which has a pinion 16a formed on its tip and a flange 16b for dust-proof and water-proof. 17 is a stopper fitted at the rear portion of the pinion shaft 16, 18 is a bearing disposed at the inner surface of the clutch inner member 13 for supporting the rear portion of the pinion shaft 16, and the bearing 18 supports the front end of the return spring 19 of the pinion shaft 16. When the pinion shaft 16 is moved forward, the spring 19 is deflected by the stopper 17, and the forward movement is completed when the stopper 17 abuts against the rear end face 13b of the clutch inner member 13.
Reference numeral 20 is a solenoid switch connected to the rear bracket 9 by means of bolts, the solenoid switch 20 having a forward driving function in which the pinion shaft 16 and a switching function in which the contacts are closed upon closure of a key switch for allowing the power supply from the battery to the electric motor.
In the conventional engine starter apparatus as above described, the armature 1 of the d.c. electric motor generally comprises an armature winding having four coil conductor sections inserted in each slot 2a by double wave-winding in every slot pair located at a predetermined interval in the plurality of slots 2a formed in the outer circumference of the armature core 2 as illustrated in FIGS. 2 and 3 and by providing two double wave-wound coils 1a in one slot 2a so that four coil conductor sections are disposed within each slot 2a.
However, since the conventional engine starter apparatus comprises a d.c. electric motor of which the armature 1 has the construction that four coil conductor sections are disposed within each of the slots 2a of the armature core 2, the slots 2a need to have a relatively large depth sufficient for receiving four coil conductor sections in a single slot 2a. This makes it impossible to make the diameter of the armature rotary shaft 3 large and imposes a limitation in the radial size of the over-running clutch within the rotary shaft. There has been a problem in that the use of this kind of starter apparatus in certain large dispacement engines requiring a high torque to start is difficult from the view point of mechanical strength and durability.
Also, since the diameter of the armature rotary shaft 3 cannot be made large for the above reasons, the clutch outer member of the over-running clutch mechanism must be arranged in common or in a unitary structure with the shaft portion of the armature rotary shaft 3, so that the assembly of the rollers 12 are very difficult, resulting in a cause of the low productivity.